1. Field of the Invention
The present invention relates generally to a process and apparatus for automatic positioning of a piece, such as a support for electronic components on a worktable where the support must be precisely positioned in a determined position with respect to a reference system carried by the table, the invention relates more particularly to a serigraphic machine for automatic positioning of a substrate on a worktable of the machine for the manufacture of connection circuits formed by multiple thick layers deposited on the substrate before mounting and connecting electronic components between the layers by connecting circuits.
2. Description of the Prior Art
In a general way, industrial products in numerous applications require tools which are very precise and assembly processes for mounting components wherein a minimum of play exists between the pieces used in the process. In all these cases, the precision of manufacture or of mounting is equally conditioned by the precision of the positioning of pieces, one with respect to the others, and more generally by the position of pieces to be worked vis-a-vis on a support or worktable utilized during the course of manufacture or the course of mounting.
In the electronic industry primarily and with the object of realizing circuits still more perfect and for assembling them in ever reducing volumes, the manufacturers have been led to utilize microplates of integrated circuits more commonly referred to as microchips or "chips" and to mount these chips on substrates of which the conductors or conductive layers are distributed in several separate planes, insulated one from the others, by insulating layers except at certain predetermined points where conductive columns assure the electric connections between conductors or conductive layers situated in different planes.
Fabrication of these substrates is generally done using a serigraphic machine which permits depositing on an insulating electric support, for example, alumina, a series of layers alternately conductive and insulating, each layer being obtained by application to a screen on which the transparent portions correspond to that of the layer to be obtained, of a pasty material which is either conductive or insulating.
To be able to obtain electric connections between conductors situated in different planes, it is indispensable that the screens which are mounted successively in the serigraphic machine to depose these layers be positioned with very great precision, one with respect to the others. It is equally important that the support in the serigraphic machine which is used each time to receive a layer should be perfectly positioned with respect to the screen.
In U.S. Pat. No. 4,236,301, there is described means for positioning a substrate on a movable worktable comprising a horizontal support plateau of a substrate. These means include a reference system of three points constituted by three rollers fixed in position for rotation around vertical axes. This cartesian reference system has a first axis defined by two rollers, while the second axis perpendicular to the first axis passes by the third roller. This second axis places the first axis outside of the portion of the axis comprised between the two rollers defining the first axis.
To position the substrate with respect to this reference system, that is to apply two lateral adjacent sides of the substrate against these three rollers (two rollers for a side and the third roller for the other lateral side), three supplementary rollers or pressure rollers are provided capable of free pivoting around a vertical axis for displacement in an opening of a support plateau to maintain the substrate against the three rollers of the reference system. In other words, the substrate is positioned on the support plateau against the three rollers of the reference system, and through the use of a manual control system, three pressure rollers are moved to maintain the substate in contact with the three rollers of the reference system.